I have to admit that I was wrong today. I always thought that sideloading was possible on any Android device. And I failed to install any apps on this phone.
The phone comes with Android 2.1. It partially seems to be some kind of CFW, as the kernel name is a bit weird and there is an app for adjusting root access after a factory reset.
But let's go back to sideloading. Since the phone has very little internal memory available (around 150 MB), I first tried installing apps via ADB. I enabled USB debugging and tried to connect the phone to the PC. Unfortunately, there is no ADB device connected and the phone does not connect as any kind of storage either.
I tried many times to get it working, but I didn't succeed at all. So this method is impossible for me, at least for now.
The second approach was simply to put the .apk files on a microSD card, plug it into the phone and install the apps from there. I failed again. When I opened the file browser on the phone, I was unable to install any .apk files as the phone said it had "no application to open this file".
Honestly, I'm lost. For now, I'm giving up because I can't see a way to install any apps on that phone.
It's a shame, because the phone is a really nice piece of hardware from a time when smartphones weren't all the same. As you can see from the screenshots, it is quite unusual, and it has a lot of hardware buttons. Most of them are useless, but it's still nice that the phone is different.
Jan "Jenkings" Škoda - blog
Simplifying IT, Amplifying Knowledge